TOKYO —Nine Japanese nationals have joined Islamic State, Japan’s former Air Self-Defense Force chief Toshio Tamogami quoted a senior Israeli government official as saying, but the government’s top spokesman said on Friday it had not confirmed the information.

Tamogami, now a senior official of a tiny new political party, said on his blog that Nissim Ben Shitrit, the director-general of Israel’s foreign ministry, told him this month that nine Japanese had joined Islamic State.

Asked about the possible participation of Japanese citizens in the militant group, Chief Cabinet Secretary Yoshihide Suga told a regular news conference, “The government has not confirmed such information.”

No one was immediately available for comment at the Israeli embassy in Tokyo, at the Israeli foreign ministry or at the Japanese foreign ministry.

Tamogami told Reuters that no details besides the number of Japanese participants were given to him in his meeting with Nissim Ben Shitrit, a former ambassador to Japan.

About 1,000 recruits from a vast region stretching from India to the Pacific may have joined Islamic State to fight in Syria or Iraq, the head of the U.S. Armed Forces’ Pacific Command, Admiral Samuel Locklear, said on Thursday.

His comment came as a threat by Philippine militants to kill a German hostage, in a show of solidarity with Islamic State, has stoked fresh concern the Middle East group’s brand of radicalism is winning recruits in Asia and posing a growing security risk in the region.